This invention is related to a junction-breakdown protection semiconductor device, especially for protection of a shallow junction under a high voltage or high current condition.
Currently, the higher packing density of a semiconductor device, the smaller the device size which is used. Also, due to geometrical effects of semiconductor devices (e.g. the short channel effect, the narrow width effect, and so on), vertical dimensions are so small that the diffused junction depth reaches is as small as 0.25 .mu.m.
But semiconductor devices of shallow junction depth have been fabricated without consideration of the junction breakdown between the metal conductor and shallow junction caused by a high input voltage or high input current. For example, in high packing density semiconductor memory devices composed of field effect transistors, an input protection circuit or gate protection circuit is connected to the input pad for prevention of isolation breakdown of internal transistors caused by electrostatic discharge.
Especially, in the input protection circuit composed of diffused resistors or clamp diodes, the connection between the wire bonding pad and the diffused layer of the semiconductor device is formed as an ohmic connection by a metal conductor.
But because of the ohmic connection edge made by an etching process or a defect of the semiconductor substrate itself, or by a pit or spike on the semiconductor surface in the ohmic connection region between said metal conductor and diffused junction, or by a high voltage caused by an electrostatic discharge which is input of said metal conductor, the junction of said connection area may burn out, and semiconductor the substrate and said metal conductor will become a short circuit. This is because the strong electric field caused by the voltage difference between the semiconductor substrate, which is typically at ground potential, and said metal conductor to which a high voltage is applied is applied to said edge, pit or spike.
Short circuit phenomena caused by said junction breakdown between the metal conductor and the substrate occur not only at the ohmic connection area between the input pad and the diffused layer but also at ohmic the connection area between metal the conductor and the diffusion area, which is a boost node which accommodates high current in semiconductor devices. For example, in semiconductor devices designed for 5 volt operation, a short-circuited junction can be caused by strong a electric field confined to a surface spike or pit at the ohmic connection area of the boost node where the operating voltage is boosted to 8 volt.